1. Technical Field
The present invention relates to a semiconductor device and a method for cutting electric fuse, and particularly relates to a semiconductor device including an electric fuse and a method for cutting such electric fuse.
2. Related Art
A technology is conventionally known, in which a fuse is mounted in a semiconductor device, and the fuse is cut, so that a value of a resistor employed in the semiconductor device is suitably adjusted, or a failure element is separated and replaced into a normal element.
Typical manner for cutting a fuse includes cutting a fuse by irradiating a laser beam in a portion of the fuse and cutting a fuse by applying an electric current.
U.S. Pat. No. 4,064,493, Japanese Laid-open patent publication No. 2005-39,220 and Japanese Laid-open patent publication No. 2005-57,186 disclose an electric fuse, which is capable of being cut by utilizing a phenomenon, in which a material constituting the electric fuse migrates by an electromigration.
Japanese Laid-open patent publication No. 2005-39,220 discloses an electric fuse, which is breakable with a smaller current. In Japanese Laid-open patent publication No. 2005-39,220, an electric conductor constituting an electric fuse is formed to have a geometry that the conductor is turned back for several folds. FIG. 9 is a plan view, showing an electric fuse disclosed in Japanese Laid-open patent publication No. 2005-39,220. In this case, a fuse 1100 includes two folds of turn-back.
The fuse 1100 includes a current inflow terminal 1101 and a current drain terminal 1102, and further includes a first forward path straight line 1103, a return path straight line 1104 and a second forward path straight line 1113 between both of the terminals. The fuse 1100 further includes a first perpendicular coupling portion 1106, which provides a coupling between the first forward path straight line 1103 and the return path straight line 1104, and a second perpendicular coupling portion 1107, which provides a coupling between the second forward path straight line 1113 and the return path straight line 1104. When a predetermined current is supplied from current inflow terminal 1101 into current drain terminal 1102 in the fuse 1100 having the above-described configuration, the heats generated in the hatched portions 1108 outside of the fuse 1100 are added to the heats generated in the hatched portions 1109 inside of the fuse 1100, accelerating the cutting of the return path straight line 1104 sandwiched with the hatched portions 1109. This provides easily cutting the fuse 1100.
Moreover, Japanese Laid-open patent publication No. 2005-57,186 has disclosed a configuration in which, when a current is flowed in a fuse, heat generated in a portion of the fuse, which is to be cut, is trapped or accumulated in the neighborhood of the portion in the fuse, which is to be cut, by enclosing the portion with a plate.
Japanese Laid-open patent publication No. 2004-186,590 discloses a semiconductor device, which is provided with an electrically conducting layer and an insulating film formed in this order in or above a semiconductor substrate, and also provided with a connecting hole that extends through the insulating film and reaches an upper surface of the conducting layer. The semiconductor device includes an interconnect layer, which includes a flat portion formed on the insulating film and a curved portion formed integrally with the flat portion and formed on a side surface and a bottom surface of the connecting hole, the curved portion defining a hollow portion that has a geometry tapered toward an upside thereof. In this case, a geometry of the interconnect layer formed in the connecting hole is curved, and have a reduced thickness in the lower portion of the connecting hole. The structure of such interconnect layer is a fuse element structure, and a resistivity thereof is increased as the thickness is reduced, so that a minimum current value for cutting an electrical coupling between the lower interconnect layer and the overlying interconnect layer can be reduced. It is described that such configuration provides a simultaneous pursuit of a suitable fuse element structure, which is capable of being cut with a smaller current density, and a suitable multiple-layered interconnect structure.
Japanese Laid-open patent publication No. 2004-214,580 discloses a layout of a fuse for providing an improved production yield and reliability by reducing a defective cutting of a fuse. A fuse layout described in Japanese Laid-open patent publication No. 2004-214,580 is shown in FIG. 10. In a fuse layout 1010, which is composed of an interconnect electrode having a barrier metal layer composed of a refractory metal and a principal interconnect metallic layer, a plurality of meltdown type fuse units 1011 and 1012 that are connected in series are formed. In addition, a fuse pad 1013 is formed in one end of the fuse unit 1011, a fuse pad 1014 is formed in a coupling portion of the fuse unit 1011 and the fuse unit 1012, and a fuse pad 1015 is formed in the other end of the fuse unit 1012. In order to flow an electric current through the fuse unit 1011, an electrical voltage is applied across the fuse pad 1013 and the fuse pad 1014. In order to flow an electric current through the fuse unit 1012, an electrical voltage is applied across the fuse pad 1014 and the fuse pad 1015. If at least one of the plurality of fuse units is broken in such fuse layout 1010, this is equivalent that the whole layout is cut, and therefore rate of occurring a defective cutting can be greatly reduced.
The present inventor has recognized as follows. As described above, the cutting of the conventional electric fuse is generally achieved by applying an electrical voltage across the both ends of the fuse link to be cut to achieve a passage of an electric current through the fuse link. Nevertheless, when an electric current is applied to a fuse link to break thereof, an incomplete cutting of the fuse link is often caused to occur a defective cutting. If such defective cutting of a fuse link is occurred, the electric fuse acquires a lukewarm electric resistance. Therefore, a problem is caused, in which a decision circuit decided that the fuse is not cut, in case that it must be decided that the fuse is cut. On the other hand, since the electric fuse acquires an increased electric resistance, a level of an electric current that requires for cutting the fuse can not be flowed when an electric current is flowed once again to break the fuse link.